As part of continuing efforts in the art to formulate high performance, cost-effective detergent products, it is necessary to obtain accurate and reproducible data for the performance of different detergent components and formulations in applications which call for the removal of different types of common soils. The reliability of methods available for the quantitative determination of soil removal is in many cases a limiting factor in these efforts. It is the object of this invention to provide a method having enhanced reliability and versatility for determining the performance of detergents in the removal of proteinaceous soils.
A number of methods are known and commonly used to measure soil removal in detergent performance studies. Of particular relevance to the present invention are methods which center upon measurements of light reflectance from clean, soiled, and laundered fabric swatches. Under such methods, reflectance is first measured for fresh, clean fabric swatches, then for swatches which have been soiled with controlled amounts of one or more soils, and finally for swatches which have been soiled and then laundered with the test detergent under controlled conditions. Comparison of the three sets of reflectance measurements provides a quantitative determination of the performance of the detergent. (Description of such reflectance tests are found, for example, in the text Detergency, vol. 5, part 1, Surfactant Science Series, edited by G. Culter and R. C. Davis, Marcel Dekker, Inc. publisher, New York 1972, pp. 323-448.) Also of particular relevance are methods in which fabric swatches are soiled with a soil containing a radioactive tracer element. In these cases, counting of the soiled fabric radioactivity before and after laundering provides the measure of soil removal. (See, for further description of such methods, the publications of B. E. Gordon and E. L. Bastian, J. Am. Oil Chem. Soc., vol. 45, pp. 754-759; B. E. Gordon, J. Roddewig, and W. T. Shebs, J. Am. Oil Chem. Soc., vol. 44, pp. 289-294; W. T. Shebs and B. E. Gordon, J. Am. Oil Chem. Soc., vol. 45, pp. 377-380; and B. E. Gordon and W. T. Shebs, J. Am. Oil. Chem. Soc., vol. 46, pp. 537-543.) Under conventional practice, radiolabelling of soils for detergency testing is a technique which has been applied only to non-proteinaceous oily soils and to clay soils.